Ethylene-α-olefin copolymers are molded into a film, sheet, bottle or the like by various molding methods, and subjected to various applications such as a food packaging material and the like.
Among ethylene-α-olefin copolymers, copolymers polymerized using a metallocene catalyst are known to have excellent mechanical strengths such as impact strength, tensile strength and the like. Thus, these copolymers have been investigated to be utilized in various applications since weight reduction and cost reduction of a molded article can be expected while maintaining mechanical strengths, by rendering the molded article thinner. However, an ethylene-α-olefin copolymer polymerized using a conventional metallocene catalyst shows high extrusion load in extrusion processing, and manifests small melt tension and swell ratio, thus, molding processability thereof is not sufficient and its utilization is limited.
In contrast, recently, a novel metallocene catalyst has been investigated, and an ethylene-α-olefin copolymer having improved molding processability polymerized using this catalyst has been suggested. For example, JP-A No. 2003-96125 describes an ethylene-α-olefin copolymer polymerized using a metallocene catalyst composed of a transition metal compound having a ligand prepared by connecting of two groups having a cyclopentadiene type anion skeleton via a crosslinking group, a transition metal compound having two groups having a substituted cyclopentadiene type anion skeleton not mutually connected, and a cocatalyst component for activation. JP-A No. 2004-149761 describes an ethylene-α-olefin copolymer polymerized using a metallocene catalyst composed of racemic-ethylenebis(1-indenyl)zirconium diphenoxide; triisobutylaluminum; and a cocatalyst component prepared by contacting of silica, hexamethyldisilazane, diethylzinc, pentafluorophenol and water. JP-A No. 2006-233206 describes an ethylene-α-olefin copolymer polymerized using a metallocene catalyst combining a transition metal compound having a ligand prepared by connecting of two groups having a cyclopentadiene type anion skeleton via a crosslinking group with a transition metal compound having a ligand prepared by connecting a group having a cyclopentadiene type anion skeleton and a group having a fluorenyl type anion skeleton via a crosslinking group; and a carrier prepared by supporting methylalumoxane as a cocatalyst on porous silica.
However, the ethylene-α-olefin copolymers described in JP-A No. 2003-96125 and JP-A No. 2004-149761 are not yet sufficiently satisfactory in extrusion load and swell ratio in molding processing, and the ethylene-α-olefin copolymer described in JP-A No. 2006-233206 has still insufficient swell ratio, and additionally, the molten ethylene-α-olefin copolymer molecular chain has a long relaxation time, thus, the appearance of a molded article obtained by molding and the taking-up property in molding are not yet sufficiently satisfactory.